The present invention relates to the general field of turboprops including at least one set of adjustable-pitch fan blades. More particularly, the invention relates to controlling the pitch of the fan blades of a two-propeller airplane turboprop.
In known manner, a two-propeller airplane turboprop comprises a turbine having two contrarotating rotors, each driving a set of unducted fan blades. By way of example, reference may be made to document GB 2 129 502 that describes various embodiments of such a turboprop.
In a turboprop of this type, the pitch of the fan blades in each set (where pitch may also be referred to as orientation) constitutes one of the parameters enabling the thrust of the turboprop to be controlled. For this purpose, a known solution for controlling the pitch of the fan blades in a given set consists in using a pitch control takeoff via radial shafts that are actuated by actuators situated at the center of the turboprop.
Although effective, that solution nevertheless presents the drawback of being particularly complex to make since it requires the use of a large amount of gearing. Furthermore, that type of control requires radial shafts of large diameter in order to overcome the torsion problems to which they are subjected. Unfortunately, such shafts give rise to a large maximum cross-section, thereby giving rise to additional obstruction in the stream of air flowing through the turbine, and thereby giving rise to a loss of efficiency.